A frequent problem in food processing is the loss of aroma and/or flavor volatiles. In the case of coffee, these volatiles can be lost at a number of points in the processing. One point is when the coffee beans are roasted. See U.S. Pat. No. 2,087,602 to McCrosson, Issued July 20, 1937, which discloses a process for enriching the aroma and flavor of coffee by drenching roast and ground coffee with aroma-laden gases liberated during green bean roasting in a sealed coffee roaster. Roasting produces gaseous aromas which are generally harsh and unpleasant-smelling but can be fractionated to recover useful aroma volatiles. See U.S. Pat. No. 2,156,212 to Wendt et al, issued Apr. 25, 1939, which discloses a process wherein vapors from roaster gases are collected and purified and then contacted with liquid coffee concentrate, coffee powder or roast and ground coffee.
Another point where aroma volatiles are lost is during the grinding of the roasted beans. Although grinding is necessary to liberate solubles for extraction, a substantial portion (about 50%) of the aroma volatiles are frequently lost. See U.S. Pat. No. 2,306,061 to Johnston, issued Dec. 12, 1942, wherein compounds or vapors released during grinding of roasted coffee are brought into contact with coffee or beverage extract, e.g. soluble coffee, in a vessel cooled to -70.degree. C. (-94.degree. F.) to -15.degree. C. (-20.degree. F.) by dry ice or brine.
Another point where aroma volatiles can be lost is during milling of coffee to produce flaked coffee. Although flaked coffee has increased extractability, the aroma intensity of the coffee is much less than that of roast and ground coffee due to loss of aroma volatiles (about 75% of total available) liberated during milling. See U.S. Pat. No. 3,615,667 to Joffe, issued Oct. 26, 1971, wherein flaked low and intermediate grade coffees which are poor in aroma quality are combined with high grade coffees having good aroma qualities.
Two principal methods are used to correct the problem of aroma volatile loss in coffee processing. The first method involves low temperature grinding to prevent excessive release of aroma volatiles. One example is the grinding of roasted coffee beans in the presence of liquid nitrogen. See British Patent Document No. 1,424,264 to Strobel, published Feb. 11, 1976. Another example is the co-grinding of coffee beans with dry ice. See U.S. Pat. No. 3,725,076 to Stefanucci et al, issued Apr. 3, 1973.
Low temperature grinding to prevent excessive release of aroma volatiles has a number of disadvantages. In the case of liquid nitrogen grinding, special equipment is necessary, adding to the expense of the processing. Also, the aroma character of the volatiles produced during low temperature grinding can be significantly different from aroma volatiles produced by grinding at ambient temperatures. Further, there is a practical limit to the amount of volatiles which can be retained.
The other principal method for dealing with the problem of the loss of aroma volatiles is by recovery thereof on an aroma substrate. One example is direct condensation of gaseous volatiles on a chilled aroma substrate, as suggested by the Johnson patent. Typically, cryogenic temperatures (below -150.degree. F.) are employed. See U.S. application Ser. No. 957,384 to Edmund P. Pultinas, filed Nov. 3, 1978, commonly assigned, which discloses a method for forming highly aromatized coffee products by adsorbing grinder gas onto a packed column of coffee cooled by liquid nitrogen. See also U.S. Pat. No. 3,823,241 to Patel et al, issued July 9, 1974, wherein an absorbent carrier is cooled to at least -40.degree. F. (preferably -150.degree. F.) and then placed in communication with roast and ground coffee under pressure conditions which transfer the coffee aroma to the absorbent carrier. Another example is aroma frost equilibration with an aroma substrate which is typically a liquid glyceride such as coffee oil. See U.S. Pat. No. 3,783,163 to Patel, issued Jan. 1, 1974, which discloses a method for aromatizing edible oils by adding the oil to a cryogenic fluid to form a slurry, adding an aroma frost to the slurry, preferably with mixing, and then allowing the mixture to equilibrate to evaporate the cryogenic fluid, leaving behind a residue of aroma-enhanced oil.
The use of liquid nitrogen for volatile recovery, as in the case of liquid nitrogen grinding, results in high capital and operational cost for large-scale processes because of the heat transfer limitations of conventional liquid nitrogen processing. For example, in the case of aroma frost equilibration with coffee, the standard equipment for forming the aroma frost is a scrapped-wall heat exchanger. The wall of the exchanger generally serves as a heat transfer barrier, thus necessitating liquid nitrogen as the coolant to offset this heat transfer problem. Even where liquid nitrogen is used, significant heat transfer limitations can remain. For example, in the case of direct condensation of gaseous aroma volatiles onto a packed column of coffee, thermal gradients are created because of low effective bed thermal conductivity of the packed column which result in non-uniform adsorption of the volatiles onto the coffee.
Further, the low temperatures created by liquid nitrogen processing tend to magnify the heat transfer problems. The volatile stream used in direct condensation or aroma frost formulation usually contains predominant amounts of other compounds. For example, a grinder gas stream of coffee aroma normally contains 85% air, 3% water, 12% CO.sub.2 and only 0.1% aroma volatiles. These other compounds can condense at liquid nitrogen temperatures, thus creating an additional sensible heat load which necessitates the use of more liquid nitrogen at an additional cost.
A suitable method for direct condensation of food volatiles on a solid food substrate is described in a U.S. patent application to Gordon K. Stipp and Hing C. Tse, Ser. No. 088,249, filed Oct. 25, 1979, now abandoned, entitled "Method for the Collection of Aroma Volatiles Onto a Food Aroma Substrate", commonly assigned. A particulate mixture of solid coolant such as dry ice and food substrate such as coffee is rapidly agitated while in contact with food volatiles, preferably coffee aroma, which adsorb onto the mixture. The coolant is then vaporized to provide an aromatized food product. This process enables direct absorption of coffee aroma on a solid coffee substrate at significantly higher temperatures, e.g. -110.degree. F. to -80.degree. F. where dry ice is the solid coolant, than are possible with liquid nitrogen processing because of improved heat transfer characteristics.
The process described in the Stipp et al application is an economical and efficient method for direct condensation of volatiles on a solid food substrate. However, this process does have a couple of requirements which can create some inflexibility. The number of commercially available solid coolants is limited. Also, the solid coolant must be vaporized or removed from the aromatized solid food substrate which can lead to volatile stripping. Further, where dry ice is employed as the coolant, a sharp aroma is imparted to the substrate which may be undesirable for some food materials. In addition, lower, e.g. liquid nitrogen, temperatures are sometimes necessary for maintaining the aroma profile of certain volatile mixtures. Commercially practical methods for direct condensation of gaseous volatiles, especially coffee aroma, on a solid aroma substrate, especially solid, particulated coffee oil, at cryogenic temperatures are still needed.
It is therefore an object of the present invention to provide a process for direct condensation of gaseous volatiles on a solid food substrate at cryogenic temperatures which has improved heat transfer characteristics during condensation/adsorption of the volatiles on the substrate.
It is a further object of the present invention to provide a process for direct condensation of gaseous volatiles on a solid food substrate at cryogenic temperatures which is efficient and economical.
It is yet a further object of the present invention to provide a process for direct condensation of gaseous volatiles on a solid food substrate at cryogenic temperatures which is commercially practical.
It is yet another object of the present invention to provide a process for direct condensation of gaseous aroma on a solid food substrate at cryogenic temperatures which results in an aromatized product having good fidelity aroma.
These and further objects of the present invention are disclosed hereafter.